It is similar in appearance to a fiddle or violin but larger (in its earlier forms essentially a modified vielle), which employs key-actuated tangents along the neck to change the pitch during play, much like a hurdy-gurdy.

While historically not too common an instrument in Sweden (relatively speaking), the violin outshining it in usage among spelmän (players of Swedish folk music), the nyckelharpa became a popular folk instrument in the Swedish province of Uppland during the 17th century, subsequently leading to its popularization and spread throughout Sweden the following centuries.

The earliest of these is found in a 1408 fresco by Taddeo di Bartolo at the Palazzo Pubblico chapel in Siena, Italy, which depicts an angel playing a "keyed viola".

Such were popular in Southwestern Europe and eventually evolved into the solo-played "symphonia"-hurdy-gurdy in France or Spain in the 1200s, featuring diatonic tangents.

The earliest possible depiction of nyckelharpor known, or rather "keyed vielles" by appearance, can be found in a relief on one of the portals to the Källunge Church, located on the Swedish island of Gotland.

[7][8] The earliest confirmed depiction of a nyckelharpa appears in an Italian church painting found in Siena, Italy, dating to 1408.

Starting from the early 17th century, however, the nyckelharpa got a foothold as a popular folk instrument among spelmän (players of Swedish folk music) in the Swedish province of Uppland, which came to be the stronghold for nyckelharpa music the following centuries, including musicians like Byss-Calle [sv] (Carl Ersson Bössa, 1783–1847) from Älvkarleby.

[3] The popularization of the nyckelharpa continued and by the early 20th century it had become an archetypal instrument for Swedish folk music, equivalent to the violin.

[8] Composer, player and maker of nyckelharpor Eric Sahlström (1912–1986) used this new instrument and helped to re-popularize it in the mid-20th century.

[citation needed] The 1960s and 1970s saw a resurgence in the popularity of the nyckelharpa, with notable artists such as Marco Ambrosini (Italy and Germany), Sture Sahlström, Gille, Peter Puma Hedlund and Nils Nordström including the nyckelharpa in both early music and contemporary music offerings.

It has also been used in non-Scandinavian musical contexts, for example by the Spanish player Ana Alcaide, the English singer and multi-instrumentalist Anna Tam, and Sandra Schmitt of Storm Seeker, a pirate metal band from Germany.

This now is a yearly event taking place on the Sunday closest to 26 April – this being the birthday of the great nyckelharpa player Byss-Calle.

[5] The popularisation of the Italian design has led other luthiers in recent years to produce reproductions of the depiction as well.

Didier François, a violinist and nyckelharpist from Belgium, is noted for using an unusual playing posture, holding the nyckelharpa vertically in front of the chest.

Some players may use a violin bracket to keep the nyckelharpa away from the body so that it can swing freely, causing it to sound more "open" as its resonance is not damped.